[LLVMdev] #APP/#NOAPP

[Eric Christopher]

On Mon, May 6, 2013 at 3:08 PM, reed kotler <rkotler at mips.com> wrote:
> Hi Hal,
>
>
> I think that it's perfectly valid to generate inline assembler and it
> looks 1000 times cleaner than if I tried to do this same work with
> selection DAG.
>

I'm pretty sure you're the only one who thinks this. What's so
complicated about doing this either at selection dag or MI lowering
time?

-eric

>> I hope you don't mind if I play devil's advocate here...
>>
>> Why is this so complicated that it would be messy to do, at least in part,
>> at a lower level? I can understand needing IR-level analysis for some kinds
>> of transformations, but late IR-level passes can insert target-specific
>> intrinsics, those can be matched to pseudo instructions, and those pseudo
>> instructions can be expanded (as late as necessary) by a custom inserter. I
>> agree that this may add more boiler-plate work, but it is not immediately
>> obvious why this would be 1000x messier.
>>
>>   -Hal
>
> I should probably qualify this with "1000 times messier for me" :)
>
> In this case the whole problem fit neatly in a simple IR level module pass.
>
> I had to create an alternate calling convention for one part but otherwise
> this IR
> pass made an otherwise very messy problem easy to implement.
>
> Reed
>
>
>>> There are other stubs to be created for other parts of the mips32
>>> port.
>>>
>>> So I'd like to get a solution to these ugly APP/NOAPP markers.
>>>
>>> Maybe you would not do things this way but I think it's a perfectly
>>> valid approach.
>>> No two people have 100% the same idea of what is best practices.
>>>
>>> The following kind of patch works without adding a mode to asm
>>> printer
>>> but in general is harder
>>> for people to use since they have to get a hook to MCAsm in order to
>>> change the inline_asm_start/end
>>> strings. (In AsmPrinter) on a per function basis.
>>>
>>>     if (OutStreamer.hasRawTextSupport() &&
>>>     MAI->getInlineAsmStart()[0])
>>>       OutStreamer.EmitRawText(Twine("\t")+MAI->getCommentString()+
>>>                               MAI->getInlineAsmStart());
>>>
>>> So a simple method in AsmPrinter would be the easiest for people to
>>> use.
>>>
>>> It just turns off the APP/NOAPP markers which we should be able to do
>>> anyway; it's independent of the discussion regarding the goodness or
>>> not
>>> of the compiler emitting inline assembly.
>>>
>>>
>>> Reed
>>>
>>>
>>>
>>>>> Alternately I could change the logic in AsmPrinter to not print a
>>>>> line if
>>>>> the inlline asm start/end string is null.
>>>>>
>>>>> ????
>>>>>
>>>>> TIA.
>>>>>
>>>>> Reed
>>>>>
>>>> Cheers,
>>>> Rafael
>>>
>>>
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>
>
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